The present invention relates to a solid image-pickup device represented by a C-MOS, a CCD, etc. and a method of manufacturing the same, particularly, to a solid image-pickup device that permits improving the sensitivity and suppressing the smear by increasing the effective opening rate of a micro lens and a method of manufacturing the same.
The solid image-pickup device comprises the regions contributing to passing the light trough the light receiving element and opto-electric conversion, hereinafter referred to each of the regions as “open portion”. In general, the sensitivity of the light receiving element depends on the size of the open portion. In other words, the small open portion leads to a low sensitivity. The open portion of the light receiving element such as a CCD is limited to about 20 to 40% of the entire area of the element. In general, the sensitivity is increased by forming a micro lens with height opening rate on a light receiving element, in addition to the measure for increasing the open portion as much as possible, because the micro lens with height opening rate improves the light collection. Note that opening rate of a lens is defined as the ratio of the area of the plan view of a micro lens to the square of the pitch between the adjacent micro lenses.
In recent years, a high precision solid image-pickup device having more than 2,000,000 pixels is being propagated. In such a high precision solid image-pickup device, plurality of miniaturized light receiving elements are arranged densely. Consequently, the reduction of the opening rate based on the miniaturization of the light receiving element and the reduction in sensitivity accompanying the reduction in the opening rate are prominent.
As described above, the micro lens is useful means to improve the opening rate of the solid image-pickup device. The high precision solid image-pickup device having more than 2,000,000 pixels requires the arrangement of the micro lenses at a pitch not larger than 5 μm and not larger than 0.3 μm of the gap between the adjacent micro lenses, hereinafter referred to as “a lens gap”. However, the micro lens is formed in general by utilizing in combination the photolithography using a photosensitive resin and a heat flow technology. Because of the restrictions of these technologies, the lens gap in the side direction of the micro lens is about 1 μm to at most about 0.4 μm. If the lens gap is made 0.3 μm or less in heat flow process, the adjacent micro lenses are connected to each other at the lens edge and the nonuniformity of the photosensitive resin tends to occur, resulting in failure to provide a stable production technology of a mass production level. The restrictions inherent in the prior art described above lead to the lens gap larger than 0.3 μm. That is, it is one of the important subjects that the reduction in the opening rate of the micro lens accompanying the high precision of the solid image-pickup device, in other words, the sensitivity of the solid image-pickup device is lowered.
Concerning conventional formation of the micro lens, various technologies are disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 60-53073 and Japanese Patent Disclosure No. 5-48057. The technology of the formation of the micro lens disclosed therein is following.
Japanese Patent Disclosure No. 60-53073 discloses the technology of forming a lens hemispherical by utilizing the heat flowability (heat flow) of resin caused by the heat flow. Also disclosed in detail is the technology of working a lens by some etching technologies. In addition, disclosed is formation of an organic film such as PGMA and an inorganic film such as OCD (SiO2 series) on the lens surface.
Each of Japanese Patent Disclosure No. 5-48057 and Japanese Patent Disclosure No. 60-53073 discloses the technology of laminating a thin film on a resin lens, said thin film differing from the lens material in the refractive index. Specifically, Japanese Patent Disclosure No. 5-48057 discloses the depositing method using CVD of, for example, ECR plasma, the method isotropically depositing an inorganic film or a resin film on a resin lens to perform a small gap between lenses and improve the opening rate of the lenses. In general, the method of synthetic vapor deposition for depositing, for example, a urea resin by using a vapor deposition machine is also useful to perform a small gap between lenses.
However, these prior arts necessitate a costly vacuum apparatus and a CVD apparatus and are not simple process, leading to a marked increase in the manufacturing cost.
As a stable production technology capable of improving the light collection or as a production technology capable of forming the shape between the adjacent micro lenses, Japanese Patent Disclosure No. 60-53073 referred to previously, Japanese Patent Disclosure No. 6-112459 and Japanese Patent Disclosure No. 9-45884 disclose a technology called trench system utilizing an etching. These technologies certainly make it possible to product a concave lens by forming a concave portion between adjacent micro lenses and the edge of the concave portion circular.
However, in the trench system, it is difficult to form a small gap between the adjacent micro lenses not larger than 0.3 μm. This is the reason why the trench system is the technology to form a concave portion by etching such as a dry etching with a micro lens used as a matrix, the lens is basically shaped moderate and, at the same time, the etching is performed such that the concave portion is widened. In other words, the trench system is not basically directed to the technology in such a manner to perform the small gap between the adjacent micro lenses by etching such as a isotropic etching or an anisotropic etching with a micro lens used as a matrix.